The present invention relates generally to applying currents and making electrical measurements on cylindrical members such as pipes. More particularly it relates to facilitating the engagement or attachment of multiple electrodes or contacts to the external surface of a pipe and also to facilitating removal of such multiple electrical contacts from a pipe surface.
Studies have been made as part of an overall effort to improve the performance of pipes and other such structures relative to damage from flaws in the structures which can lead to cracking in the walls thereof. One of the types of cracking which has received and which deserves special attention is stress corrosion cracking. Such type of cracking occurs where the pipe element serves to contain high temperature, high pressure steam, water, or other fluids.
One way which has been very effective in studying the cracking which occurs within a pipe wall is by making electrical measurements of the pipe and observing changes in electrical potential and flow of current in the pipe both before and after the cracking has been initiated and as the crack grows.
To study the cracking phenomena within pipe walls and other elements, it is frequently desirable to make many measurements essentially around the entire circumference of the pipe and also to make similar measurements along the length of the pipe from one contact point to another spaced axially along the length of the pipe.
Where the application of a large number of current patterns and the measurement of a large numbers of voltages on pipe members can be accomplished, the data which is generated from such measurements can be used in the so called Electric Current Computed Tomography or ECCT. ECCT is a practice in which determination can be made of the condition of the pipe itself from the electrical measurements made with the aid of the many surface contacts which are attached to the pipe.
Accordingly, a central problem in the use of the ECCT technology is the making of a large number of electrical contacts precisely on a pipe surface to permit the application of currents and the measurement of voltages and the critical data to be collected. The present method is one for facilitating the rapid attachment of a large number of contacts to a pipe surface and the removal of the large number of contacts from a pipe surface.
What is needed in connection with making ECCT measurements of piping is reliable electrical contact of many elements at a pipe surface. The contact to be effective electrically, must be one which does not change with time. Further the contacts must be evenly spaced both along the pipe and about the pipe in order to provide the proper geometry to accumulate the data needed for ECCT type of analysis and study.
Alternatively, the method can be applied to the measurement of voltages as part of techniques where current attachments are made external to the fixture.